Impulse Radar Uses Clockless Approach

Various approaches promise to compensate for the system issues encountered during the use of traditional digital design techniques. For example, Novelda accomplished this goal by leveraging the continuous-time-binary-valued (CTBV) design paradigm. In a white paper titled, "Nanoscale Impulse Radar," the firm's Nikolaj Andersen and Tor Sverre (Bassen) Lande explain this approach and its impact on the company's radar system.

The 12-page document begins by providing background into Novelda's impulse radar sensor. This electromagnetic (EM) sensor, which is embedded in standard CMOS silicon, requires no clock. In today's processor technologies, the synchronous clocked design reduces both power consumption and speed. In fact, for some high-end processors, close to 50 percent of the total power budget is consumed for clock distribution.

Because it is "clockless," the CTBV design paradigm saves most of the energy required for driving an on-chip clock. Computation sequencing is achieved using inherent gate delays instead of synchronous clocks. To perform high-resolution ranging, the impulse-radar technology uses very short microwave pulses with durations below 1 ns. It is therefore suitable for high-resolution ranging, which works at both short and long distances.

In this case, the sampler has to capture a signal at several gigahertz. With a conventional approach, this would require running high-speed clocks and consuming large amounts of power and silicon. Instead of continuously sampling the received signal, however, Novelda employs a strobed-sampling concept.

For each pulse that is transmitted, the backscattered EM energy is sampled after a given time offset. This offset represents the time of flight of the signal relative to the time of transmission, which can in turn be used to represent the distance to the remote object. The core circuitry of this impulse radar's strobed sampler operates in the continuous time domain without any clock. By keeping the received signal in the continuous time domain for as long as possible, distance measurement accuracy in the picoseconds range is enabled.

As mentioned, the basic strobed sampler is extended by exploring the domain of CTBV coding, as the CTBV signal has near-infinite resolution in the time domain. To recreate the incoming analog signal as digital values that can be represented in a computer, the signal is converted using swept threshold sampling rather than a single threshold in the quantizer. For each threshold step, the conversion result is accumulated in a digital counter. With its unique approach, this impulse radar paves the way toward adding a large processing gain early in the processing chain.